On Sat, Dec 04, 2010 at 04:11:40AM +1100, Nick Piggin wrote:> > Alternatively, what about switching brd away from overloading BLKFLSBUF> > to a real implementation of (overloaded) BLKDISCARD support in brd.c?> > One that doesn't blindly nuke the entire device but that properly> > processes the discard request.> > Yeah the situation really sucks (mkfs.jfs doesn't work on ramdisk> for the same reason).> > I want to unfortunately keep ioctl for compatibility, but adding new> saner ones would be welcome. Also, having a non-default config or> load time parameter for brd, to skip the special case, if that would> help testing on older userspace.

How many programs actually depend on BLKFLSBUF dropping the pages usedin /dev/ram? The fact that it did this at all was a historicalaccident of how the original /dev/ram was implemented (in the buffercache directly), and not anything that was intended. I think that'ssomething that we should be able to fix, since the number of programsthat knowly operate on the ramdisk is quite small. Just a few systemprograms used by distributions in their early boot scripts....

So I would argue for dropping the "special" behavior of BLKFLSBUF for/dev/ram.